1. Field of the Invention
The present invention relates to a toner for developing electrostatically charged images. More particularly, it relates to an electrostatic toner having improved fixing in a hot roll fixing copy system, and further relates to prevention of copy quality deterioration in copy machines equipped with an automatic double sided copy device or an automatic sorter device.
2. Prior Art
Heretofore, copy machines including a thermal fixing system need to have at least a definite fixing strength for the toner used therein.
Copy machines, especially those equipped with an automatic double sided copy device or an automatic sorter have disadvantages such that double sided copies have poor quality and that in the case where the copies are sorted in an automatic sorter, the back sides of the copies become smudged when the fixing strength of the toner is not properly adjusted. In order to solve such disadvantages, toners containing polyethylene wax, natural wax such as carnauba wax or the like, ethylene/vinyl acetate copolymer, and the like have been employed.
These conventional toners containing polyethylene wax or natural wax cause so-called filming, which is the result of wax fixing to the surface of the carrier or the sensitizing material to become a film due to the failure of dispersion of the wax in the binder resin, or due to the elimination of the wax. The filming causes various effects such as smudged images and the like.
In addition, these conventional toners containing ethylene/vinyl acetate copolymer have a disadvantage such that the storage stability of the toner sometimes deteriorates (the powder material is blocking at the elevated temperature) due to ethylene/vinyl acetate copolymer fixing itself.